Acids and BasesAcids and Bases

An IntroductionAn Introduction

IntroductionIntroduction

Inorganic and organic acids are Inorganic and organic acids are important industrial chemicals; in important industrial chemicals; in 2002, H2002, H22SOSO44 was the number 1 was the number 1 chemical produced in the U.S.:chemical produced in the U.S.:

36,000,000 metric tons 36,000,000 metric tons (80,000,000,000 lbs)(80,000,000,000 lbs)

1metric ton = 1000Kg = 2204.6lbs1metric ton = 1000Kg = 2204.6lbs

Common Household Common Household AcidsAcids

Some common household acids:Some common household acids:

Vinegar CH3COOH

Citric acid

Ascorbic acid

O

HO

HO

O

OH

O OH

O

HO

OH

OH

HO

OO

HO

Common Household Acids Common Household Acids and Basesand Bases

Common Household Common Household BasesBases

Some common household bases:Some common household bases: Ammonia - NHAmmonia - NH3 3 (cleaners)(cleaners) Sodium hydroxide – NaOH (oven Sodium hydroxide – NaOH (oven

cleaner and drain cleaner)cleaner and drain cleaner) Calcium oxide – CaO (cement)Calcium oxide – CaO (cement)

Physical PropertiesPhysical Properties

Physical properties of acids:Physical properties of acids: Sour/tart tasteSour/tart taste Pricking/stinging sensation on the Pricking/stinging sensation on the

skinskin blue to red litmus paperblue to red litmus paper

Physical properties of bases:Physical properties of bases: Bitter tasteBitter taste Slippery to touchSlippery to touch red to blue litmus paperred to blue litmus paper

Acid Base TheoriesAcid Base Theories

The great theoristsThe great theorists

Definitions of Acids and Definitions of Acids and BasesBases

ArrheniusArrheniusAcidAcid: produce H+ in : produce H+ in waterwater

Ex. HCl hydrochloric Ex. HCl hydrochloric acidacid

BaseBase: produce OH- in : produce OH- in waterwater

Ex. NaOH sodium Ex. NaOH sodium hydroxidehydroxide

Definition of Acids and Definition of Acids and BasesBases

Brondsted-LowryBrondsted-Lowry

Acid: donates Acid: donates a protona proton

Base: accepts Base: accepts a protona proton

H+, H has no H+, H has no neutrons so this neutrons so this is a protonis a proton

Definition of Acids and Definition of Acids and BasesBases

LewisLewis

Acid: electron pair acceptorAcid: electron pair acceptor

Base: electron pair donorBase: electron pair donor

BFBF33 F F NH3NH3 H H

F : BF : B H : N: H : N:

FF H H

Can accept e-Can accept e- Can donate e-Can donate e-

Ammonia; NHAmmonia; NH33

Strong AcidsStrong Acids

For the equation:For the equation:

HX (aq) HX (aq) H+ (aq) + X- (aq) H+ (aq) + X- (aq)HX is the acidHX is the acid

For exampleFor example

HCl (aq) HCl (aq) H+ (aq) + Cl – (aq) H+ (aq) + Cl – (aq)

In strong acids, this reaction goes to completion In strong acids, this reaction goes to completion (only products are left, none of the reactants (only products are left, none of the reactants remain)remain)

Strong AcidsStrong Acids

The Big 6 Acids:The Big 6 Acids: HClHCl hydrochloric acidhydrochloric acid HH22SOSO44 sulfuric acidsulfuric acid

HNOHNO33 nitric acidnitric acid

HH33POPO44 phosphoric acidphosphoric acid HFHF hydrofluoric acidhydrofluoric acid HClOHClO44 Perchloric acidPerchloric acid

Weak Acids, ex. Weak Acids, ex. CHCH33COOHCOOH

EquilibriumEquilibrium

Ka = Ka = [H+][Cl-[H+][Cl-]] [HCl][HCl]

Ka is the equilibrium constant for acids (a Ka is the equilibrium constant for acids (a measure of the relative strength of an acid)measure of the relative strength of an acid)

[ ] means concentration in moles/liter or [ ] means concentration in moles/liter or MolarityMolarity

For strong acids, the Ka is so large that is For strong acids, the Ka is so large that is cannot be measured, because the acids cannot be measured, because the acids completely, totally dissociatescompletely, totally dissociates

Weak Acids Have Ka < 1Weak Acids Have Ka < 1

HSOHSO44-- hydrogen sulfate ion 1.2 x 10 hydrogen sulfate ion 1.2 x 10 -2-2

HClOHClO22 chlorous acid chlorous acid 1.2 x 10 1.2 x 10 -2-2

HNOHNO22 nitrous acid nitrous acid 4.0 a 10 4.0 a 10 -4-4

HCN hydrocynaic acidHCN hydrocynaic acid 6.2 x 10 6.2 x 10 -10-10

NHNH44++ ammonium ionammonium ion 5.6 z 10 5.6 z 10 -10-10

HOCHOC66HH55 phenol phenol 1.6 x 101.6 x 10-10-10

Note: Bases are very weak acidsNote: Bases are very weak acids

Strong BasesStrong Bases

Strong Bases are like strong acids: Strong Bases are like strong acids: they dissociate completely they dissociate completely

HB HB B+ + OH- B+ + OH-

For exampleFor example

KOH KOH K+ + OH- K+ + OH-

Weak Bases, Ex. NHWeak Bases, Ex. NH33

The Kb is just like the KaThe Kb is just like the Ka

Kb = Kb = [B+][OH-][B+][OH-]

[BOH][BOH]

*B is not Boron, but from HB *B is not Boron, but from HB B+ + B+ + OH-OH-

Kb is the equilibrium constant of a baseKb is the equilibrium constant of a base

[ ] is concentration in Molarity [ ] is concentration in Molarity (mole/liter)(mole/liter)

Molarity is moles Molarity is moles per literper liter

Convert given masses into Convert given masses into moles (if in grams) and moles (if in grams) and

volume into liters (if given in volume into liters (if given in something other than Liters)something other than Liters)

“Mole Stew”- how many moles are in a liter of water

Measuring Measuring Concentration of Concentration of

HydrogenHydrogenpH = -log [H+]pH = -log [H+]

Find the pH if [H+] = 1.00 x 10Find the pH if [H+] = 1.00 x 10-5-5

How about the pH if the [H+] = 5.43 x 10How about the pH if the [H+] = 5.43 x 10 -3-3

pOH = - log [OH-]pOH = - log [OH-]

Find the pOH if [OH-] = 3.78 x 10 Find the pOH if [OH-] = 3.78 x 10 -8-8

How about the pOH if [OH-] = 8.99 x 10 How about the pOH if [OH-] = 8.99 x 10 -2-2

What would the pH of each of these be?What would the pH of each of these be?

pH ScalepH Scalehttp://www.youtube.com/watch?v=3otQdpMfiRg

http://www.youtube.com/watch?v=YvnwiP1u8-A

Stop notes here Stop notes here for nowfor now

We’ll continue another day.We’ll continue another day.

Thanks!Thanks!

Acid-Base IndicatorsAcid-Base Indicators

Common Indicators:Common Indicators:

Phenolphtalein pink in basePhenolphtalein pink in base clear in acidclear in acidLitmus PaperLitmus Paper red red blue blue bluebluered red Bromthymol blue pH 3 green pH 4.5 blueBromthymol blue pH 3 green pH 4.5 blueMethyl red Methyl red pink in acid pink in acid yellow in baseyellow in base

There is an indicator for every purposeThere is an indicator for every purposehttp://www.youtube.com/watch?v=vrOUdoS2BtQ

pH IndicatorspH Indicators

pH MeterpH Meter pH meters, unlike pH meters, unlike

indicators, directly indicators, directly measure the measure the concentration of H+ concentration of H+ ions. They do this ions. They do this by measuring the by measuring the electrical conduction electrical conduction of the solution.of the solution.

Why will the solution Why will the solution with more H+ with more H+ conduct electricity conduct electricity better?better?

Acid Base ReactionsAcid Base Reactions

Salts are produced by an acid/base Salts are produced by an acid/base neutralization:neutralization:

22HCl + Ca(OH)HCl + Ca(OH)22 → → 22HH22O + CaClO + CaCl2 2 ← salt← salt HH22SOSO44 + + 22NaOH NaOH → → NaNa22SOSO44 + + 22HH22OO

salt salt

What is a salt??What is a salt??

pH = -log[HpH = -log[H++] ] 1010-[H+]-[H+]

pH < 7 = acidicpH < 7 = acidicpH 7 > = basicpH 7 > = basicpH = 7 = neutralpH = 7 = neutral

http://www.youtube.com/watch?v=PCM5IwJ8wcs

Acid-Base TitrationsAcid-Base TitrationsTitrations are done to find the Titrations are done to find the

molarity molarity of the acid or the of the acid or the base. base.

A buret A buret (a long graduated (a long graduated cylinder ) is cylinder ) is

attached to the ring stand with a attached to the ring stand with a buret clampburet clamp..

Liquid can be delivered by Liquid can be delivered by turningturning

the the stopcockstopcock..http://www.youtube.com/watch?v=sFpFCPTDv2w&feature=related

Setting up a titrationSetting up a titration

Usually the acid is Usually the acid is placed in the flask placed in the flask with an indicator with an indicator that will change that will change color at pH = 7. color at pH = 7.

Phenolphthalein is Phenolphthalein is often used. often used. Why is Why is phenolphthalein a phenolphthalein a good choice?good choice?

Filling the buretFilling the buret

After rinsing with After rinsing with bothboth

deionized water and deionized water and base.base.

Base is then placed Base is then placed in thein the

buret. buret.

Why is this done Why is this done over the sink?over the sink?

Filling the buretFilling the buret

Open the stopcock, Open the stopcock, using a beaker to using a beaker to catch any excess catch any excess base, and let the base, and let the base level drop to base level drop to the top line (zero the top line (zero line) on the buret. line) on the buret.

Reading the buretReading the buret

The buret is The buret is graduated so that graduated so that the amount of base the amount of base delivered can be delivered can be easily measured.easily measured.

Read it as you Read it as you would a graduated would a graduated cylinder (at eye cylinder (at eye level, from the level, from the bottom of the bottom of the meniscus)meniscus)

Doing the titrationDoing the titration

The base is slowly The base is slowly added to the acid added to the acid while mixing while mixing

Finding the endpointFinding the endpoint

until the solution until the solution hits the hits the

endpoint.endpoint.

Note that the Note that the solution is solution is barelybarely pink. A dark pink pink. A dark pink means that too means that too much base has much base has been added.been added.

What is an What is an endpoint?endpoint?

The point in a titration when no more titrant should be The point in a titration when no more titrant should be added. Determined by a COLOR CHANGE.added. Determined by a COLOR CHANGE.

Equivalence points is determined by StoichiometryEquivalence points is determined by Stoichiometry

Acid-Base Titration Acid-Base Titration CalculationsCalculations

If we used 20 ml of 3.0 M HCl, how many If we used 20 ml of 3.0 M HCl, how many ml ofml of

3.0 M NaOH would we expect to need?3.0 M NaOH would we expect to need?

HCl + NaOH HCl + NaOH NaOH + H NaOH + H22OO

20 ml 3.0 mol HCl 1 mol NaOH20 ml 3.0 mol HCl 1 mol NaOH 1 L 1 L = = 20 ml20 ml 1 L1 L 1 mol HCl 3.0 mol NaOH 1 mol HCl 3.0 mol NaOH

Acid-Base TitrationsAcid-Base Titrations

So, what if you use 24.5 ml of 0.15 M So, what if you use 24.5 ml of 0.15 M NaOH to neutralize 50.0 ml of 2.5 M NaOH to neutralize 50.0 ml of 2.5 M HH22SOSO44? What is the concentration of the ? What is the concentration of the NaOH?NaOH?

2NaOH + H2NaOH + H22SOSO44 Na Na22SOSO44 + 2H + 2H22OO

50.0 ml 2.5 mol H50.0 ml 2.5 mol H22SOSO44 2 mol NaOH 1 L 2 mol NaOH 1 L

1 L 1 L 1 mol H 1 mol H22SOSO44 24.5 ml 24.5 ml

What unit will the answer be in?What unit will the answer be in? How many sig figs can we report?How many sig figs can we report?

Acid NomenclatureAcid Nomenclature

Binary AcidsBinary AcidsPrefix hydro-Prefix hydro- suffix -ic acidsuffix -ic acid

HClHCl hydrochloric acidhydrochloric acid

HIHI hydroiodic acidhydroiodic acid

HSHS hydrosulfuric acidhydrosulfuric acid

Acid NomenclatureAcid Nomenclature

TernaryTernaryCommon form --icCommon form --ic

HSOHSO44, HClO, HClO33, HNO, HNO33

Sulfuric, chloric and nitricSulfuric, chloric and nitric

One fewer oxygen -ousOne fewer oxygen -ousTwo fewer oxygen hypo-- and -ousTwo fewer oxygen hypo-- and -ousOne more oxygen per- and --icOne more oxygen per- and --ic

Acid RainAcid RainWhat is Acid Rain?What is Acid Rain?http://www.youtube.com/watch?v=HE6Y0iEuXMQ

SOSO2 and NO and NO22/NO/NO33 from from industry and cars industry and cars

ProduceProduce

HH22SOSO44 and HNO and HNO33 when when combined with watercombined with water

Can fall as rain, snow Can fall as rain, snow and as solid and as solid depositiondeposition

Where does Acid Rain Where does Acid Rain Fall?Fall?

What are the effects?What are the effects?

Forest depletion: Forest depletion: tree deathtree death

Can be seen in Can be seen in NH in White NH in White MountainsMountains

Clear lakes due to acid rain: clear becauseNo plants or fish or other life is in the lake

Statues like this Statues like this one, show one, show corrosion due to corrosion due to acid rain.acid rain.

Copper and marble Copper and marble are both acted on are both acted on by acidby acid

Effects of Acid RainEffects of Acid Rain Maple sugar Maple sugar

production in the production in the Northeast may be Northeast may be down due to acid rain: down due to acid rain: this is projected to this is projected to continuecontinue

Car paints have had to Car paints have had to be reformulated and be reformulated and there are many there are many products on the products on the market to repair market to repair damagedamage